Utility companies distribute power to customers using a network of cables, switching stations and switchgear. Switchgear is high voltage (e.g. 5 kV-38 kV) equipment, typically subsurface, vault, or pad mounted and used to distribute and control power distribution in relatively small areas. Historically, switchgear is a box or container that includes bushings, insulation, a bus bar system and a collection of active switching elements. An active switching element is a device with an internal active component, such as a fuse, a switch, or an interrupter, and external points of connection. In some active switching elements, these external points of connection are bushings. Active switching elements are used to automatically, manually, or remotely open and/or close a circuit. It should be noted that active switching elements that include switches or interrupters often include contacts in a vacuum, air, insulating oil, or dielectric gas. Distribution cables are coupled to the bushings of the switchgear and have the capacity to transmit power at high voltages. The bushings in turn are coupled to, or form an integral part of, the active switching elements inside the switchgear. The active switching elements are coupled by a bus bar system to create the switchgear.
FIG. 1 shows a common switchgear configuration 100 with source side door 110 in an open position. Latch(es) 111a and/or 111b are used to lock source side door 110 in a closed position. Inside door 110 is a front-plate 130 that forms one side of the container. In FIG. 1, the front-plate 130 is a vertical surface of the container. Coming up from the bottom of switchgear 100 are cables 112a-112f that each typically carry power in three phases from two different sources. More specifically, cables 112a-112c carry, respectively, the A, B and C phases of power from source 1, and cables 112d-112f carry, respectively, the C, B and A phases of power from source 2.
Cables 112a-112f are coupled to front-plate 130 and switchgear 100 through connectors 114a-114f. A connector or connector body is a component for connecting a power cable or bus bar to a bushing. Connectors can be straight or bent, live-break or dead-break, load-break, bolted, or probe and contact. Connectors 114a-114f are coupled to bushings extending through the front-plate 130. These bushings are coupled to active switching elements inside switchgear 100. The bushings represented in FIG. 1 are in a single plane that is horizontal to the pad. An exemplary connector is the “PUSH-OP™ Dead break Connector Catalog No. 600-13” manufactured by Cooper Power Systems, the specification of which is incorporated by reference. An exemplary bushing is Cooper Power System's “600 A 15 and 25 KV Class Deadbreak PUSH-OP™ Apparatus Bushing” (Electrical Apparatus Catalog No. 800-46), the specification of which is incorporated by reference.
Additional features may include switch handles 116a and 116b that operate switches (the active elements) inside switchgear 100 to disconnect and connect the bushings extending through front-plate 130 from the internal bus bar system. The cables 112a-112c may be disconnected from internal bus bar system by manipulating handle 116a. Similarly, cables 112d-112f may be disconnected from the internal bus bar system by manipulating handle 116b. Handles 116a and 116b are mounted onto front-plate or working surface 130 as shown in FIG. 1. It should be noted that alternative switchgear may use alternative active switching elements such as fault interrupters and fuses. It should also be noted that the front-plate or working surface 130 is a plane on the switchgear 100.
One use of switchgear is to segregate a network of power distribution cables into sections. That is, by manually opening or closing a switch (either locally or remotely), such as the switch coupled to handle 116a, the power supplied from one source to the switchgear is prevented from being conducted to the other side of the switchgear and/or to the bus. Similarly, when switch 116b is opened, power on one side of the switchgear is prevented from being conducted to the other side of the switchgear and to the bus and the taps. In this manner, a utility company is able to segregate a portion of the network for maintenance, either by choice, through the opening of a switch, or automatically for safety, through the use of a fuse or fault interrupter, depending on the type of active switching elements included in the switchgear.
FIG. 2 shows switchgear 100 with tap side door 220 open. Latch(es) 211a and/or 211b are used to lock tap side door 220 in the closed position. Inside door 220 is a front-plate or working surface 240, which is also one vertical side of the container. Coming up from the bottom of switchgear 100 are typically six cables 212a-212f that each typically carry one phase of power away from switchgear 100. In particular, cable 212a carries A phase power, cable 212b carries B phase power and cable 212c carries C phase power. Similarly, cable 212d carries C phase power, cable 212e carries B phase power and cable 212f carries A phase power. Connectors 214a-214f connect cables 212a-212f to switchgear 100 through bushings (not visible in this figure). Exemplary connectors and bushings can be the same as those described in conjunction with FIG. 1. It should be noted that the exemplary switchgear in FIGS. 1 and 2 shows one type of phase configuration. The phase configuration shown in FIGS. 1 and 2 is ABC CBA. Other phase configurations include AA BB CC. Still other configurations have one or more sources and taps on the same front plate or each on its own front plate or on the sides of the switchgear on one or more additional front plates. It should also be noted that each phase may be designated by a number, such as 1, 2 and 3, and that the switchgear may accommodate more that three phases of power. Thus, a switchgear may have a configuration of 123456 654321.
It should also be noted that there are other places at which to locate the bushings on the switchgear. The orientation of the bushings, whether mounted onto the front, side, top or back of a frame, and thereby protruding toward an exterior working space of the switchgear, is called the bushing plane. For the switchgear shown in FIGS. 1 and 2, the front plates 130 and 240 are two bushing planes for the switchgear 100.
One structure not shown in FIGS. 1 and 2 is a frame. A frame is internal to the switchgear and provides support for the active switching elements as well as the bus bar system. In other words, the frame holds the active switching elements and bus bar system in place once they are coupled to the frame. The frame is oriented to allow portions of the active switching elements, typically bushings, to protrude as a bushing plane so that connections to cables can be made.
A way is a three-phase or single-phase circuit connection to a bus, which contains combinations of switches and/or protective devices. A way may carry power in either a single-phase system or a multi-phase system. The circuit connection may or may not include active switching elements. The switchgear shown in FIGS. 1 and 2 is four-way or 4W. That is, the switchgear has connections for two sources and two protected taps.
Handle 216a operates switches inside switchgear 100 to disconnect cables 212a, 212b and 212c from the internal bus bar system. Similarly, handles 216b-216d each operate a switch inside switchgear 100 to disconnect and connect, respectively, one of individual cables 212d-212f from the internal bus bar system. Alternate switchgear can use other active switching elements such as fuses and fault interrupters.
If fuses were implemented instead of switches, the switch handles shown in FIG. 1 would be replaced by hot stick operable to access removable fuse wells that extend through front-plate 240 to allow a technician to access and/or replace the fuse.
A cut-away side view of switchgear 100 is shown in FIG. 3. As previously described, switchgear 100 in this example includes switching and/or protective devices 305 and 310 and a bus bar system 315. Devices 305 and 310 include bushings 305a and 310a for coupling to connectors 114a and 214f. Devices 305 and 310 also include bushings 305b and 310b for coupling to bus bar system 315. It should be noted that bushings 305a, 305b, 310a and 310b may be integral to or separate from switching and/or protective devices 305 and 310 and they may include mechanical or push-on connectors. A mechanical connector connects two or more metallic elements by using threaded, crimp, or wedge connections. Typical mechanical bus connections consist of two or more conductors made from bars or braids which are secured together with a threaded bolt extending through holes in a flattened portion and secured by a bolt and a conductive member with internal threads. A typical mechanical connector to a flat bus conductor surface is accomplished by threading a conductive member with internal threads onto a threaded stud or a bolt. Push-on connectors consist of two or more metallic bus conductors that can be axially joined. The components consist of a matching set of probes, rods, or ‘male’ conductors that mate with finger-contacts, bores, or ‘female’ conductors or contacts.
FIG. 4 shows a cross sectional front view of a conventional bus bar system 315. Conventional bus bar system 315 includes three copper, aluminum or other electrically conductive metal bars 415a, 415b and 415c. As shown in FIG. 4, metal bar 415a is formed or bent around metal bar 415b and metal bar 415b is similarly formed or bent around metal bar 415c. The metal bars may be flexible or partially flexible to allow connection to two rigid members. The purpose of bus bar system 315 is to conduct power from the source side active switching elements to the tap side active switching elements. Thus, if one of the active switching elements opens such that a source side or tap side cable is disconnected from the bus bar system, the remaining source and tap side cables remain connected and can transmit power.
Insulation is provided between the bus bars and the active switching elements to prevent electrical arcing. There are three common types of insulation typically used in conventional switchgear: oil, sulfur hexafluoride (SF6) gas, and air. Each type of insulation insulates each part of the switchgear from the other parts of the switchgear (bus bar and active switching elements), and from the outer surfaces of the container of the switchgear.